Guidance on best management practices for removal of anti-fouling coatings from ships, including TBT hull paints
The Marine Environment Protection Committee, at its fifty-ninth session (13 to 17 July 2009), approved the “Guidance on best management practices for removal of anti-fouling coatings from ships, including TBT hull paints”, developed by the Consultative Meetings of the London Convention and Protocol, as set out at the annex.
Member Governments are invited to bring this circular to the attention of all parties concerned.
Anti-fouling systems are used on ships’ hulls to limit the effect fouling can have on drag, fuel consumption, and the emission of combustion products. They may contain pesticides or be pesticide-free. The pesticides tributyltin (TBT) and copper are the most common anti-fouling biocides, although the shipping industry is moving away from TBT systems.
The most effective biocidal anti-fouling systems are formulated as self-polishing polymer coatings that wear away as the ship is propelled through the water, to expose a fresh layer of biocide. Biocides that leach into water from ship hulls may adversely affect non-target organisms.
Anti-fouling coating removal activities can be another major source for the release of TBT to the environment.
The choice of anti-fouling system, and collection, treatment, and disposal of spent coatings have an impact on the release of biocides into the environment, and may result in high concentrations of biocides in the marine sediments in areas close to where application and removal activities are conducted. The adoption of sound management practices for the application and removal of anti-fouling systems can reduce the release of biocides into the natural environment.
By their nature, all anti-fouling biocides are toxic and can affect a broad range of organisms beyond those that cause fouling. TBT causes reproductive anomalies and population effects in certain species of marine snails at concentrations in the parts-per-trillion range, and has been implicated in endocrine effects on other organisms.
Oysters exposed to low levels of TBT can develop shell deformities that reduce their value as seafood. TBT is associated with immune suppression and other adverse effects in other marine species, is slow to degrade, and is very persistent in sediments, where many affected species live and feed.
The International Convention on the Control of Harmful Anti-Fouling Systems on Ships (AFS Convention), which entered into force on 17 September 2008, prohibits the use of organotin biocides in anti-fouling paints used on ships. As a consequence, ships will have to either replace or overcoat their existing organotin-based anti-fouling systems.
If the large amount of TBT-containing waste that is expected to be generated at shipyards and other facilities as owner/operators attempt to achieve compliance is not properly managed, it will adversely affect the quality of bottom sediments in nearby waters.
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